Process Safety Applications for

Emerging Issues in the Gas Industry

Dr. M. Sam Mannan, PE, CSP, DHC

Regents Professor and Director

Holder of T. Michael O’Connor Chair I

Mary Kay O’Connor Process Safety Center

Artie McFerrin Department of Chemical Engineering

Texas A&M University System

College Station, Texas 77843-3122, USA

mannan@tamu.edu, +1 (979) 862-3985

http://psc.tamu.edu

Outline

Gas Exploration Hazards: Well Integrity

and Blowout Modeling

Transportation Hazards of Natural Gas

LNG Hazards as Transportation Fuels

LNG Hazard Assessment and Mitigation

Changes in LNG Terminals

1. Gas Exploration Hazards: Well

Integrity and Blowout Modeling

Well Integrity and Blowout

Modeling

Compromised

Well Integrity

Cement

Casing

Packers

Valves (e.g.,

GLV,

Shoetrack)

BOP

Safety aspects:

-Dangerous operating

conditions

-Fire/Explosion

-Increased probability

of an incident

-Protective barriers

are compromised

Environmental

aspects:

-Oil/gas spill

-Toxicity and

exposure

-Wildlife impact

Worst Case:

Blowout

Single Phase

Multiphase

Flow-rate

Decay rate

Consequence

Modeling:

Gas dispersion

Plume modeling

Fire/Explosion

Well Integrity and Blowout

Modeling

Research Focused on Two areas:

– Well Integrity Modeling

• Improve understanding and modeling of the

phenomena during well integrity issues

• Develop models that facilitate or improve the design

of safer operating and testing procedures

– Blowout Modeling

• Quantify, from science-based governing equations,

the flow rate, either single or multiphase flow, and

decay of flow rate from an uncontrolled blowout.

Well Integrity – Sustained Casing

Pressure

Sustained Casing Pressure (SCP) Model: Predicts the

behavior of gas migrating through an annulus in wells

and that serves as a tool to determine the permeability

of damaged cement.

Analytic model for gas buildup, Inherently safer testing,

Quantitative estimation of cement permeability and

leakage rate.

Well Integrity – Faulty Gas-Lift

Valve (GLV) GLV leakage model: Methodology for

Determining a GLV’s integrity that avoids

retrieving the valve and relies on examining

the annular transient-pressure response.

Presents an alternative to using Acoustic

Well Sounding.

t =1 t =2 Δm

q

Well 1

Blowout Modeling – Overview

Establishes a mathematical model based

on the basic physical phenomena, such

as heat transfer and transient fluid flow

dynamics.

The analytical model can be used to

estimate blowout rate and production

loss for different types of blowout

– Single phase oil blowout

– Single phase gas blowout

– Multiphase fluid blowout

Both onshore and offshore wells are

considered in the blowout modeling

t =1 t =2

Bubbly

Churn

Slug

Single Phase

Liquid

Single Phase

Vapor

Annular

Blowout Modeling – Methodology

t =1 t =2

Formation fluid coming

from reservoir to

surroundings through wellbore

Reservoir pressure

decreasing due to

depletion of reservoir

Reservoir

– Material balance

Wellbore

– Mass balance

– Momentum balance

– Energy balance

Interactions

– Analytic equations

Blowout Modeling – Examples

Macondo Incident

– Estimation of blowout rate and volume of oil

spilled

– Sensitivity analysis owing to uncertainties in

reservoir

t =1 t =2

Permeability

(md)

Production Loss

(million STB)

25 2.57

50 3.98

100 5.13

223.7 5.71

2. Transportation Hazards of

Natural Gas

Background

Truck Accident- On June 22,

2002 at Catalonia, Spain- LNG

truck accident possible had lead to

a (BLEVE) . 1 Killed and 2

injured

Images Retreived from Planas - Cuchi et al. (2004)

Kleen Energy Power plant

Accident

Feb 7, 2010 Middletown,

Connecticut 6 killed,50 injured

Ship Accident

June 29, 1979: The

125,000 - m3 El Paso

Paul Kayser ran aground

at 19 knots under full load

in the Strait of Gibraltar.

Liquefied to LNG or Compressed to CNG?

Natural Gas

Fixed Transportation Systems Pipeline Components (Gathering, Transmission & Distribution Lines)

Compressor Stations

Metering Stations

Valves

Control Stations

Natural Gas

Portable Transportation Systems

Tanker truck

Railway Tanker

LNG/CNG carriers

Common Causes of Failure of

Pipelines External Force

– Encroachment

– Weather-Related

Corrosion

– External Causes

– Internal Causes

Defective Pipe and Welds

Equipment Malfunction and Operator Error

Natural calamities like Hurricane and Earthquake pose direct risk to pipelines

Hazards of Fixed Transportation

Systems

Leaks leading to fire hazards

Fire Hazards

– Jet Fire

– Flash Fire

– Vapor Cloud Explosion (outdoor and enclosed)

Common Cause of failure of

portable transportation systems

Collisions- Ship-ship & ship- shore, vehicles in road

transportation, collision of trains with obstacles or

other trains.

Grounding

Intentional Terrorist Attacks

Rupture in loading/offloading

operations

Hazards of Portable Transportation Systems

• Flash Fire-ignition of portions of vapor cloud before dilution to LFL

• Pool Fire- Flammable vapor cloud traces back to the pool burning vapor above liquid

• Jet Fire - compressed or liquefied gas released as jet ignites to form jet fire.

Fire Hazards

• Vapor cloud formed in a confinement can produce damaging over pressures and hence explosion

• Large fraction of heavier hydrocarbons increase likelihood

Vapor cloud Explosion

• Physical explosion caused due to sudden boiling or phase change when LNG is spilled on water

• Ranges from small pops to large blasts

Rapid phase transition

• When LNG is in direct contact with skin , damage can occur in the form of pain and numbness.

Freeze Burns

• The stratification of LNG into layers based on its varying densities due to the different components is called rollover.

• Sudden increase in tank pressure can exceed the capacity of the pressure relief valves and may damage equipment

Rollover

• an explosion caused by the rupture of a vessel containing a pressurized liquid above its boiling point

BLEVE

3. LNG Hazards as

Transportation Fuels

LNG Transportation Hazards on

Land

LNG is used in heavy-duty

vehicles, typically vehicles that

are classified as "Class 8"

(33,000 - 80,000 pounds, gross

vehicle weight).

Typical transportation

applications are

-refuse haulers

-local delivery

-transit buses.

LNG fueling station network

http://www.cleanenergyfuels.com/buildingamerica.html

LNG transport fuel Industry

Transport LNG Producers/Distributors (e.g., Clean

energy, Southeast LNG)

LNG Tanker Truck Operators (e.g., Transgas,

Southeast LNG)

LNG Vehicle Fueling Stations (e.g., Applied LNG

Technologies, Clean Energy)

LNG Vehicle Storage Tanks (e.g., Chart Inc.,

Cryogenic Fuels Inc.)

Advantage of LNG as

transportation fuel

Strong reduction of SOx and NOx emissions

Zero particulates

Reduction of CO2 emissions

LNG fueled engines have a lower noise

production

Lower dependency on oil

Gas will be dominant in the future

Hazards in using LNG as

transportation fuel

Fire on Bridge

Pooling and Brittle Failure of Bridge

Phase Change and Overpressure

-Vessel overpressure failure

-Rapid Phase Transition (RPT)

-Boiling Liquid Expanding Vapor Explosion (BLEVE)

-Vapor Cloud Explosion (VCE)

Cryogenic Burns/Frostbite

Environmental Effects

Research Problems

Assessment of LNG safety requires identification of hazards and

safeguards associated with each stage of LNG supply chain

Relative risk comparison between other fuel supply chain and LNG

supply chain is needed for assessing relative safety of LNG

LNG safety risks in road transportation is normally associated with

-Mechanical failure

-High-impact crash

-Terrorist attack

Risk Assessment of bulk delivery and fuel storage at LNG fueling

station should be performed

LNG vehicle fuel tanks are more at risk than LNG tankers due to

-Broader range of applications

-Less well-trained personnel

Research problems (contd.)

Hazards identification and consequence analysis

of LNG spill on bridges are another concern

Research should be performed on probable

consequences of :

-cryogenic deterioration of bridge material (e.g.,

concrete, anchorages, tendons)-brittle efffect

-Fire and radiation effect on bridge materials

4. LNG Hazard Assessment and

Mitigation

Outline

Introduction

LNG Risk-Based Approach for facility

siting.

LNG mitigation measures

– Passive

– Active

– Procedural

Introduction

LNG Safety Concerns

• Leaks leading to fires and explosions

• Transportation Hazards - Collisions

and Grounding

• Intentional Terrorist Attacks

• Hazards during Operation - Rupture

in loading/offloading operations

Risk Based Approach for LNG facilities

Hazard Identification

HAZOP,FMEA, What-If

Consequence Analysis

Source Models, Dispersion

Frequency Analysis

Reliability, FTA, ETA

Risk Estimation

Evaluation, Presentation

Risk Reduction

LOPA, Emergency Planning

Risk Assessment

Comparisons, Perception

Decision Making

Safe conditions

Hazard Identification

HAZOP, FMEA

Consequence & Frequency Analysis

Consequence Analysis

– Source term

modelling

– Dispersion modelling

– Fire and explosion

modelling

– Effects modelling

Frequency Analysis

– Historical data

– Analytical or

simulation techniques

– Expert Judgments.

Risk Estimation

Risk – Consequence x Frequency

Individual risks –probability of exposure of a person, system, or plant to a hazard or a particular level of the hazard. Example: risk of injury or fatality in performing work

Societal risks – frequency or probability of outcome and the number of people (or facilities) affected, by a specified consequence level from exposure to specified hazards, represented in F-N profiles

Risk Reduction

Inherent safety can be presented in all layers of protection

However, it is especially directed toward design features

34

Strategy Description

Inherent Reduce, eliminate hazards by using inherent safety

principles

Passive Features that do not need to be activated

Active Devices that need to be activated in order to avoid

the hazard or reduce the consequences

Procedural An administrative action is required

Selecting a Strategy to Reduce the

Risk Inherent

Passive

Active

Procedural

Due to the multiple hazards and technologies present in a chemical plant, a good safety program involves ALL strategies

The best time to consider and implement Inherent Safety is early in process development stage

35

Hendershot, Dennis. Research Needs For Inherently Safer Technology Workshop. Houston, TX, 2008

Generally decreasing reliability and robustness

Controlling of Hazards to Reduce Risks

Hazards that cannot be eliminated should be controlled

An acceptable level of risk is achieved by a design that

reduces the likelihood of a hazardous event occurring

or that mitigates the consequences of such an event.

When hazard elimination is not possible, the next best

options are engineered solutions. These solutions can

be either passive or active.

36

Layers of Protection Analysis

(LOPA)

A process of evaluating the effectiveness of Independent Protection Layers in reducing the likelihood or severity of an undesirable event.

Drive the consequence and/or frequency of potential incidents to an acceptable risk level using independent protection layers (IPLs)

Unacceptable Risk

Acceptable Risk Risk = frequency * consequence

The LOPA “Onion”

COMMUNITY EMERGENCY REPSONSE

PLANT EMERGENCY REPSONSE

PHYSICAL PROTECTION (DIKES)

PHYSICAL PROTECTION (RELIEF DEVICES)

AUTOMATIC ACTION SIS OR ESD

CRITICAL ALARMS, OPERATORSUPERVISION, AND MANUAL INTERVENTION

BASIC CONTROLS, PROCESS ALARMS,AND OPERATOR SUPERVISION

PROCESSDESIGN

LAH

1

I

Hierarchy of Mitigation Measures

39 … Table 1 API 752

Active Mitigation Measures

Measure Example

Ac

tive

Prevent release

(reduce frequency) Safety instrumented systems

Control size of scenario

Fire and gas/emergency shutdown systems

(reducing quantity released)

Fixed/automatic active fire fighting systems

Mitigate effect to building occupants Issue occupants with personal protective equipment

(PPE) for hazards

Fan type Fog type Conical type

Water Curtains as

Active Mitigation

Measures

Expansion foams

Expansion foam is

considered as an important

safety measures

– To control LNG fire

– To reduce downwind

vapor concentration

Procedural Mitigation Measures

Measure Example

Pro

ce

du

ral

Prevent release

(reduce frequency)

Mechanical Integrity Inspection

Permits for hot work, lockout/tagout, line

breaking, lifting, etc.

Control size of scenario Manual active fire fighting systems

Mitigate effect to building occupants

Emergency response plan including, as

appropriate: evacuation, escape routes,

shelter-in-place, etc.

Evacuate building occupants during start-up

and planned shutdowns

LNG Vapor Dispersion modeling with CFD Field test setup

Experiment design

Background – Water curtain is considered one of the most effective engineering

method in mitigation of various types of hazards

– Suggested as most economic and promising built-in safety tool for LNG vapor suppressing technique

– Major experiments in late 70s and early 80s

– No definitive and comprehensive guideline for water curtain design in LNG vapor control

– Different types of water curtains, and their ability to control LNG vapor dispersion have not been studied in detail • Underlying physical phenomena of complex interaction between water

droplet and LNG vapor cloud

Controlling LNG Vapor Cloud using Water Curtain

Experiment design

Facility: Brayton Fire Training Field

Pit 1 (3m x 3m x 1.22m) filled with water up to 1.2m

Wooden confinement (1.52m x 1.52m x 0.31m) 3 types spray: Fan, Conical and Fog

Pit1

Fan type Fog type Conical type

Dilution ratio (DR)– effectiveness of WC

Assuming const. wind speed of 5.1 m/s

Each water curtain showed different

efficiencies in different mechanisms

Controlling LNG Vapor Cloud using Water Curtain Concentration Ratio

Concentration ratio at 2.1 m Concentration ratio at 1.2 m

Concentration ratio at 0.5 m

LNG Fire Mitigation using Expansion Foam

Made in foam generators by mixing the foam solution with air to an expansion ratio, i.e., 500:1

Expansion

foam Foam

generator

LNG Fire Mitigation using Expansion Foam Fire height reduction

1. Fire before foam

application 2. Fire right after foam

application

3. Fire during foam control at

steady state

9.75 m

θ

Win

d

32 %

increase

68 %

decrease

58 %

decrease

≥ 12.80 m

Fire base

(6.40 m×10.06 m)

3.96 m

<March, 2009>

5. Changes in LNG Terminals

Regulations for LNG Terminals

LNG facilities are constructed according to Liquefied

Natural Gas Facilities: Federal Safety Standards and

regulated by Federal Energy Regulatory Commission

(FERC). Federal regulations incorporate NFPA 59A

(Prescriptive Standard)

Objective: Keep fire and explosion

hazards onsite (i.e., within the

facility boundaries) in the event of

a loss of a containment event.

Regulations for LNG Terminals

NFPA prescribes a series of 10 min duration design

spills (also called accidental leakage), in order to

analyze safety contours known as exclusion zones

based on the following parameters:

Flammability Limit

½ LFL methane (i.e., 2.5% concentration

Radiant Heat Flux

Not exceeding 5 kW/m^2

Overpressure Although NG vapor clouds are unlikely

to produce damaging overpressures

Regulations for LNG Terminals

The exclusion zones are the regions where the potential hazard exists, and the public cannot be exposed to this hazard.

FERC does not allow active systems as mitigation strategies for the exclusion zone requirements. ONLY passive systems can be implemented for the accomplish of this criteria.

During the last years, FERC has clarified its interpretation of the federal requirements. These interpretations continue its evolution due to new analytical tools and new hazard criteria.

Regulations for LNG Terminals

Risk Based Analysis

The NFPA 59A and FERC have introduced risk-based analysis approaches that represent a change from the previous prescriptive approach.

There is a new chapter named: Performance (Risk Assessment) Based LNG Plant Siting.

Therefore, Likelihood or probability scenarios are integrated within the consequences analysis in order to identify injury or fatality of population nearby.

Additionally, FERC has included vapor cloud explosions hazards of flammable refrigerant releases from liquefaction processes (regarding to export terminals), which were not present in import terminals (based on vaporization processes).

Regulations for LNG Terminals

Import Terminals

FERC implemented the 2001 edition NFPA 59A to identify single accidental release scenarios.

Two types of hazardous outcomes were considered:

• Radiant heat flux (from pool fires)

• Flammable vapor dispersion

FERC required assessment of vapor dispersion from:

• Full cross-section pipe breaks

• High pressure flashing jets

DEGADIS was the software approved to calculate the boundaries derived from the ½ LFL cloud.

Regulations for LNG Terminals

Export Terminals

Refrigeration processes and the associated plants that are used to liquefy natural gas are considerably more complicated than import regasification terminals.

Due to the limited experienced with liquefaction processes, FERC and DOT had to reevaluate their requirements.

As result of this reassessment, these were the most significant changes proposed:

• New approval methodology for vapor dispersion software tools (PHAST and FLACS were accepted).

• New method of identifying single accidental leakage sources. (based on likelihood instead of prescriptive).

• Introduction of vapor cloud explosion calculations for flammable refrigerants

Regulations for LNG Terminals

From Import to Export Terminals

Flammable refrigerants such as chlorofluorocarbons, ammonium, carbon dioxide, and non-halogenated hydrocarbons might be more reactive than NG. (i.e., ethylene can undergo vapor cloud detonation).

This new risk was not taken into account by the analysis of import terminals.

Additionally, FERC requires now to determine the zones where a 1psi overpressure can be presented in order to establish the overpressure boundary.

Conclusions

Risk Assessment – Thermal Danger Zones; Tanker Danger Zones;

Flammable vapor Danger Zones

LNG has been used as transportation fuel in

limited volume since 1970’s

There is an increase in interest for using

LNG more in different sectors due to

developments of many safety standards and

rising global gas demand

Conclusions

Though there has been fewer road incidents

associated with LNG, the risks and hazards

will be more with increasing use

Safety of LNG trailer trucks and vehicle

fuel tanks should be assessed and updated

LNG industry has had a good safety record

for the past 40 years

Research needs to respond to dynamic

situation